Title

Location

Arlington, Virginia

Session Start Date

8-11-2008

Session End Date

8-16-2008

Abstract

Almost all the bridge footings in southern California are on piles due to the soil condition. Steel (H & W), reinforced concrete and steel pipe filled with reinforced concrete are common piles that are using at bridge abutment and bent footings. Various methods and procedures are available when using known driving energy to determine the bearing capacity of the pile. These procedures can be categorized into three areas: (1) pile driving formulas, (2) wave equation analysis of pile driving, and (3) dynamic pile driving analysis. Pile driving formulas all utilize the energy delivered per blow, the resistance to movement of the pile per blow, pile penetration, and some acknowledgement of the unknown produced by all components, which act to drive the pile. All of the driving formulas make use of the conservation of energy theory: (Hammer energy) – (Energy losses) = (Work performed) (1) Soil resistance multiplied by pile penetration represents work performed, hammer stroke multiplied by ram weight represents hammer energy, and various factors and/or constants in driving formulas represent energy losses in the piling system. Gates formula is formally accepted by Caltrans to consider the pile capacity per number of blows per 300mm pile penetration. In lieu of static load test the typical method for determining load-bearing capacity of a pile depends on knowledge of the energy used to drive the pile. When the pile has been driven to the specified tip elevation but the specified bearing value as determined by the Gates formula has not been obtained the contractor is allowed to keep about a foot of the pile above the ground to do the retap after a set period. Trial and error method would be employed or minimum of 12 hours unless bearing is obtained sooner during the retap process. Application of the Gates formula is the basis of acceptance, and pile penetration is measured over the last few blows. In fact most engineers prefer to use the more conservative approach and determine the penetration by counting the number of blows per foot or half foot. The point of retap is to emphasize the ground take-up that has taken place over a given period. In this paper besides considering more than 2000 piles that some of them were accepted after retapping, the relation between the elastic rebound theory and the increment of blows over a given period will be presented.

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Aug 11th, 12:00 AMAug 16th, 12:00 AM

Pile Driving and the Elastic Rebound Theory

Arlington, Virginia

Almost all the bridge footings in southern California are on piles due to the soil condition. Steel (H & W), reinforced concrete and steel pipe filled with reinforced concrete are common piles that are using at bridge abutment and bent footings. Various methods and procedures are available when using known driving energy to determine the bearing capacity of the pile. These procedures can be categorized into three areas: (1) pile driving formulas, (2) wave equation analysis of pile driving, and (3) dynamic pile driving analysis. Pile driving formulas all utilize the energy delivered per blow, the resistance to movement of the pile per blow, pile penetration, and some acknowledgement of the unknown produced by all components, which act to drive the pile. All of the driving formulas make use of the conservation of energy theory: (Hammer energy) – (Energy losses) = (Work performed) (1) Soil resistance multiplied by pile penetration represents work performed, hammer stroke multiplied by ram weight represents hammer energy, and various factors and/or constants in driving formulas represent energy losses in the piling system. Gates formula is formally accepted by Caltrans to consider the pile capacity per number of blows per 300mm pile penetration. In lieu of static load test the typical method for determining load-bearing capacity of a pile depends on knowledge of the energy used to drive the pile. When the pile has been driven to the specified tip elevation but the specified bearing value as determined by the Gates formula has not been obtained the contractor is allowed to keep about a foot of the pile above the ground to do the retap after a set period. Trial and error method would be employed or minimum of 12 hours unless bearing is obtained sooner during the retap process. Application of the Gates formula is the basis of acceptance, and pile penetration is measured over the last few blows. In fact most engineers prefer to use the more conservative approach and determine the penetration by counting the number of blows per foot or half foot. The point of retap is to emphasize the ground take-up that has taken place over a given period. In this paper besides considering more than 2000 piles that some of them were accepted after retapping, the relation between the elastic rebound theory and the increment of blows over a given period will be presented.